1. Field of the Invention
The present invention relates to an optical signal transmission system, particularly to the optical signal transmission system which enables high-speed optical data transmission more than 1 Gbps (bit per second).
2. Description of the Related Art
In the optical signal transmission system, in order to lengthen lifetime of a vertical cavity surface emitting laser diode (hereinafter referred to as VCSEL) light source and in order to cover output of VCSEL even if electric current is lowered, an example is Japanese Patent Application Laid-Open (JP-A) No. 2003-152284. This discloses a system in which a plurality of light sources is used and the light sources are arranged within the range smaller than an end face of a light guide path.
In this technology, in order to enable the high-speed transmission not lower than 1 Gbps in multi-mode transmission, a step index type (SI type) plastic optical fiber (hereinafter referred to as POF) can not be used as the light guide path. In a perfluorinated optical fiber which is used in GI-POF (Graded Index type Plastic Optical Fiber), transmission loss is generated because mode noise is generated in the optical fiber having a relatively small diameter. Further, because the optical fiber has such a small diameter, efficient coupling from the plurality of VCSEL light sources to the end face of the light guide path is difficult, and cost becomes higher.